You just think that ole Hog you've got is huge street machine! These guys have dwarfed even the 1500-lb Dodge Tomahawk "rolling sculpture". I guess if you have a spare tank engine, and copious amounts of free time, the thing to do is build a motorcycle.
I am absolutely certain the Tomahawk kicks its ass, though- and if you factor in the value of the time to build, the approximately $100,000 US build cost of the Tomahawk may still be less than the German monstrosity.
As always, demand drives price. The nine Tomahawks sold went for $555,000 each, which is a tad on the steep side for something not street legal.